Quick Answer:
If the cold side at one faucet is weak while the hot side is fine, the problem is usually local at that fixture: a partially closed cold stop, a clogged inlet screen or cartridge, or debris in the short supply line. Start by confirming the cold shutoff is fully open, then disconnect and flush the cold supply into a bucket, clean the cold inlet screen or cartridge, and compare the cold and hot flow after cleaning.
Why This Happens
- Small screens or cartridges at the faucet inlet collect mineral scale and debris over time and restrict cold flow more than hot flow at a single fixture.
- A partially closed or faulty angle stop (cold shutoff) at the fixture isolates the cold side only, reducing flow locally.
- Debris from recent work or a failing supply hose/line can lodge at the cold inlet and block flow.
- If you see problems only on the cold side at that one fixture, stay focused on the fixture components rather than larger hot-water systems or the house supply. For related situations, see **Low pressure on hot side only at one fixture** and **Low pressure after valve replacement at fixture**.
Step-by-Step What to Do
1. Confirm the cold shutoff (stop) is fully open
- Locate the cold angle stop under the sink or behind the fixture. Turn it fully counterclockwise until it stops—don’t force it past that point.
- Open the cold faucet and check flow after this. If flow improves, the stop was partially closed or sticking.
2. Remove and inspect the aerator
- Unscrew the aerator from the faucet spout and check for sediment or a clogged screen. Rinse or soak it briefly in vinegar if mineral deposits are present.
- Test the cold flow with the aerator off to see if the restriction is at the aerator or upstream.
3. Disconnect the cold supply at the faucet and flush into a bucket
- Turn the cold angle stop to the OFF position before disconnecting fittings if the design requires it; in many cases you’ll shut the stop, disconnect the supply hose at the faucet inlet, then reopen the stop briefly to flush into a bucket. Use a bucket to catch water and avoid dumping into cabinets.
- Open the stop slowly and let water run. Strong steady flow from the supply fitting means the house side is fine and the blockage is inside the faucet. Weak or intermittent flow from the fitting indicates debris in the short supply line or a bad stop.
- Close the stop again before reconnecting any flexible lines to avoid leaks while reassembling.
4. Clean the faucet cold inlet screen or cartridge
- Follow the faucet maker’s instructions to remove the cartridge or inlet screen. If you’re unsure, remove the retaining clip or nut and pull the cartridge straight out—have a towel handy.
- Inspect screens and cartridge passages for grit, rubber bits, or scale. Rinse and soak stubborn mineral deposits in white vinegar for 15–30 minutes, then scrub gently with an old toothbrush.
- Reassemble the cartridge or screen, reconnect supply, and slowly open the stop to check flow.
5. Compare hot vs cold flow after cleaning
- Turn on both hot and cold and note any differences. If cold is now similar to hot, the local cleaning solved it.
- If cold remains weak despite a clear supply flow and clean cartridge/screen, consider repeating the flush, checking the flexible supply hose inside the cabinet for kinks, or replacing the short supply hose.
What Not to Do
- Don’t chase hot-water systems or the water heater when the symptom is cold-only at a single fixture—stay local to the fixture and its shutoff.
- Don’t replace the entire valve or faucet cartridge before confirming a clogged screen or debris isn’t the cause.
- Don’t force stuck stops or cartridges; using excessive force can break fittings and cause a bigger leak problem.
When to Call a Professional
- Call a plumber if the cold stop is stuck and won’t turn, if you encounter corrosion or broken fittings during disassembly, or if flushing and cleaning don’t restore normal cold flow.
- If multiple fixtures show low cold flow, the issue may be upstream and a professional inspection is sensible.
Safety Notes
- Have towels and a bucket ready. Close the correct shutoff before disassembling fittings to avoid uncontrolled water release.
- Wear safety glasses when flushing lines or working under the sink; debris can spray unexpectedly.
- If you’re unsure how to reassemble faucet cartridges or remove retaining clips, stop and contact a plumber to avoid damaging the fixture.
Common Homeowner Questions
- Why does only one faucet have weak cold flow?
Because the problem is usually local—angle stop, aerator, inlet screen, cartridge, or the short supply hose. - Can I clean the screen myself?
Yes. Remove the aerator and cartridge or screen, soak in vinegar if needed, rinse, and reinstall. - Will replacing the faucet fix it?
Not always. If the supply and stop are clear, a worn cartridge can cause low flow, but cleaning and replacing small parts is cheaper than replacing the whole faucet.
For more related articles, see the Low Pressure at Single Fixture hub.